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460 BCE
Democritus
Democritus was an Ancient Greek pre-Socratic philosopher who was from Abdera. -
Period: 460 BCE to 370 BCE
Democritus
Democritus was an Ancient Greek pre-Socratic philosopher who was from Abdera. He was a very important figure in the development of the atomic theory. His theory was that all material bodies are made up of indivisibly small "atoms." -
428 BCE
Plato
Plato was a Greek philosopher born in Athen during the Classical period in Ancient Greece. -
Period: 428 BCE to 348 BCE
Plato
Plato was a Greek philosopher born in Athen during the Classical period in Ancient Greece. He founded the first institution of higher learning in the European continent. He also founded the Platonist School of Thought and the Academy. According to Plato, "Reality exists away from material world, within the world of forms, which can only be viewed with the eye of the mind." They aren't really sure when he was born and when he died. This is only an estimate. -
384 BCE
Aristotle
Aristotle was a Greek philosopher and polymath. This was during the classical period in Ancient Greece. -
Period: 384 BCE to 322 BCE
Aristotle
Aristotle was a Greek philosopher and polymath. This was during the classical period in Ancient Greece. He was taught by Plato and invented the field of formal logic. He also identified the various scientific disciplines. He was a teacher that founded his own school on Athens. The school was known as the Lyceum. -
476
The Alchemists
An Alchemist is someone who versed in the art of alchemy. Alchemists tried to purify, mature, and perfect certain materials. Alchemy flourished in Greco-Roman Egypt during the Middle Ages. It moved to Europe from the 13th century to the 18th century. -
Period: 476 to 1301
The Alchemists
An Alchemist is someone who versed in the art of alchemy. Alchemists tried to purify, mature, and perfect certain materials. Alchemy flourished in Greco-Roman Egypt during the Middle Ages. It moved to Europe from the 13th century to the 18th century. -
Period: to
Lavoisier
Antonie Lavoisier is a French chemist known as the "father of modern chemistry." He discovered the role of oxygen in combustion and respiration. He also proved the law of conservation, reformed the chemical nomenclature, and named hydrogen and Oxygen. -
Period: to
John Dalton
His atomic theory suggested that all matter was comprised of indivisible and indestructible atoms with distinct masses and properties. The combination determined the physical nature of their constituent elements in 1803. -
Lavoisier
Antonie Lavoisier named Oxygen. -
Lavoisier
Antonie Lavoisier named Hydrogen. -
John Dalton
His atomic theory suggested that all matter was comprised of indivisible and indestructible atoms with distinct masses and properties. The combination determined the physical nature of their constituent elements. -
Newland's Law of Octaves
John Newland created the Law of Octaves. The Law states that when elements are arranged in the increasing order of atomic weights, every eighth element has similar properties. Basically, the properties of elements are repeated after every seventh interval. -
Period: to
Robert Millikan
He accurately determined the charge carried by an electron using the "falling-drop method." He also proved that the quantity was constant for all electrons. -
Mendeleev's Periodic Table
Dimtri Mendeleev was a Russian chemist. He arranged the elements in order of increasing weight, and he broke them into rows. He also left space for newly discovered elements. -
Photoelectric Effect
Heinrich Rudolf Hertz, a German physicist observed that when ultraviolet light shines on two metal electrodes, the voltage applied makes the voltage change. This causes sparking. -
Discovery of Radioactivity
Henri Becquerel was a French physicist. He discovered that when he placed uranium salts on top of a photographic plate, wrapped in black paper, the salt caused the plate to blacken even though there was paper in between. -
Discovery of the Electron
J.J Thomson discovered the Electron. His experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or Electrons. -
Planck's Quantum Theory of Light
Max Planck announced his finding in 1900 and in 1905. His theory shows that when light bulb filaments are heated to a certain temperature it is emitted as visible waves. -
Plum Pudding Model
J. J. Thomson created the Plum Pudding Model of an atom. The Plum Pudding Model represents an important part of the development of atomic theory. The model shows electrons surrounded by a volume of positive charge. The example he gave was "Negatively-charged plums embedded in a positively charged pudding." -
Planck's Quantum Theory of Light
Max Planck announced his finding in 1900 and in 1905. His theory shows that when light bulb filaments are heated to a certain temperature it is emitted as visible waves. -
Charge of Electrons
Robert Millikan was an Americal physicist. He measured the charge of an electron by using negatively charged oil droplets. -
Robert Millikan
He also proved that the quantity was constant for all electrons. -
Rutherford's Gold Foil Experiment
Rutherford and his co-workers, Hans Geiger and Ernest Marsden did a series of groundbreaking experiments that changed the model of an atom.
Experiment: A piece of gold foil was hit with alpha particles. Alpha particles have a positive charge. Most of the alpha particles went right through. This showed that gold atoms were mostly empty space. -
Bohr's Planetary Model
Danish physicist, Niels Bohr publishes the first series of three papers. This introduced his model of the atom. According to the model the electrons encircle the nucleus of the atom in specific allowable paths that are called orbits. -
Moseley's Atomic Numbers
Henry Moseley an English physicist publishes the atomic number paper in 1914. He found that the atomic number is the number of positive charges in the atomic nucleus. He also said that there were still three unknown elements between aluminum and gold. -
Discovery of the Proton
The Proton was discovered by Ernest Rutherford. His research resulted in a nuclear reaction that led to the first 'splitting' of the atom. He named his discovery "proton" based on the Greek word "protos" meaning first. -
Schrodinger Equation
Erwin Schrodinger created the equation. The equation helped them detect where the electron could be at any given time. -
Heisenburg Uncertainty Principle
This principle was formulated by a German physicist named Werner Heisenburg. The principle states that we can't know both the position and speed of a particle. This could be a photon or electron that has perfect accuracy. -
Discovery of the Neutron
James Chadwick conducted an experiment. He found that the new radiation was not made of gamma rays but of uncharged particles that have the same mass as a proton.